Vehicle air conditioner

ABSTRACT

A vehicle air conditioner comprising a heat pump device including a compressor that compresses refrigerant, first and second heat exchangers disposed inside the vehicle cabin within an interior air-conditioning unit, and a pressure reducing valve. The vehicle air conditioner further comprises an air-conditioning controller which controls the heat pump device and interior air-conditioning unit, an exterior heat exchanger temperature sensor and a degree-of-heating requested detecting section. If the quantity of heat absorbed by the exterior heat exchanger has decreased, the controller operates the heat pump device to operate in a mode in which a refrigerant discharged from the compressor flows through the first and second heat exchangers, bypasses the exterior heat exchanger, and then is sucked into the compressor, and a second mode in which the refrigerant is flow throughs the first heat exchanger and is bypassed around the second and exterior heat exchanger after pressure has been reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of International Application No.PCT/JP2014/001190 filed on Mar. 4, 2014, which claims priority toJapanese Patent Application No. 2013-071896 filed on Mar. 29, 2013. Theentire disclosure of this application is hereby incorporated byreference.

BACKGROUND

The present invention relates to a vehicle air conditioner to be mountedon a vehicle, and more particularly relates to an air conditioner with aheat pump device.

An air conditioner with a heat pump device has been known in the art asan air conditioner to be mounted on electric vehicles and other kinds ofvehicles. A heat pump device for use in each of those vehicles is formedby connecting together an electric compressor, an exterior heatexchanger provided outside the vehicle cabin, a pressure reducing valve,and an interior heat exchanger provided inside the vehicle cabin in thisorder via refrigerant piping (see, for example, Japanese UnexaminedPatent Publication No. 2011-5983).

When the heat pump device operates in a heating operation mode, therefrigerant is allowed to flow so that the interior heat exchangerfunctions as a radiator and the exterior heat exchanger functions as aheat absorber. On the other hand, when the heat pump device operates ina cooling operation mode, the refrigerant is allowed to flow so that theinterior heat exchanger functions as a heat absorber and the exteriorheat exchanger functions as a radiator.

Meanwhile, a vehicle air conditioner as disclosed in Japanese UnexaminedPatent Publication No. 2011-255735, for example, includes an upstreaminterior heat exchanger provided upstream in the airflow direction and adownstream interior heat exchanger provided downstream in thatdirection. Its refrigerant piping includes a four-way valve. By turningthis four-way valve, a switch is made between multiple operation modessuch as a heating operation mode and a cooling operation mode.

As another example, a vehicle air conditioner as disclosed in JapaneseUnexamined Patent Publication No. H09-240266 includes, as interior heatexchangers, an upstream interior heat exchanger provided upstream in theairflow direction and a downstream interior heat exchanger provideddownstream in that direction. The downstream interior heat exchangerfunctions as a radiator in both of heating and cooling operation modes,while the upstream interior heat exchanger functions as a heat absorberin both of the heating and cooling operation modes.

A heat pump device obtains a heating heat source from the outside air bymaking the exterior heat exchanger function as a heat absorber duringthe heating operation mode. However, in a situation where the outsideair temperature has decreased to around −20° C., for example, it isdifficult to absorb heat using the exterior heat exchanger, thus causinga significant decline in heating capacity.

To overcome such a problem, a heat source may be secured by using anelectric heater such as a PTC heater. In the case of an electricvehicle, however, the use of an electric heater increases theconsumption of a traction battery so much as to shorten its distance toempty. Likewise, in various kinds of vehicles other than electricvehicles, there is a demand for cutting down the power dissipation asmuch as possible.

In view of the foregoing background, it is therefore an object of thepresent invention to reduce the overall consumption of energy for airconditioning while maintaining comfortableness of air conditioning notonly in cooling but also in heating as well.

SUMMARY

To achieve this object, according to the present invention, if thequantity of heat absorbed by an exterior heat exchanger has decreased,the operation modes are switched into a hot gas heating operation modein which a refrigerant is allowed to flow while bypassing the exteriorheat exchanger. In that hot gas heating operation mode, the refrigerantis supposed to flow through both of first and second interior heatexchangers.

A first aspect of the present invention is a vehicle air conditionercomprising:

a heat pump device including a compressor that compresses a refrigerant,a first interior heat exchanger provided inside a vehicle cabin, asecond interior heat exchanger provided inside the vehicle cabin andupstream of the first interior heat exchanger in an airflow direction,an exterior heat exchanger provided outside the vehicle cabin, and apressure reducing valve, the heat pump device being formed by connectingtogether the compressor, the first and second interior heat exchangers,the pressure reducing valve and the exterior heat exchanger viarefrigerant piping, the heat pump device further including a bypass pipeto allow the refrigerant to flow while bypassing the exterior heatexchanger, the heat pump device being switchable between multipleoperation modes;

an interior air-conditioning unit which houses the first and secondinterior heat exchangers and which includes a blower that blowsair-conditioning air to the first and second interior heat exchangers,the interior air-conditioning unit being configured to produceconditioned air and supply the conditioned air into the vehicle cabin;and

an air-conditioning controller configured to control the heat pumpdevice and the interior air-conditioning unit.

The air conditioner further includes adecrease-in-quantity-of-heat-absorbed detecting means for determiningwhether or not the quantity of heat absorbed by the exterior heatexchanger has decreased during heating.

If the decrease-in-quantity-of-heat-absorbed detecting means has sensedthat the quantity of heat absorbed by the exterior heat exchanger isequal to or smaller than a first predetermined value, theair-conditioning controller makes the heat pump device operate in a hotgas heating operation mode including a first hot gas heating operationmode in which the refrigerant discharged from the compressor is allowedto flow through the first and second interior heat exchangers so thateach of these interior heat exchangers functions as a radiator, bypassthe exterior heat exchanger with pressure reduced by the pressurereducing valve, and then be sucked into the compressor.

According to this configuration, if the quantity of heat absorbed by anexterior heat exchanger has decreased (e.g., if the outside airtemperature has decreased to −20° C. or less), then the operation modesare switched into a hot gas heating operation mode in which arefrigerant is allowed to flow while bypassing the exterior heatexchanger, which thus allows for achieving a heating capacity withoutusing any electric heater. In addition, in a first hot gas heatingoperation mode, a high-temperature refrigerant discharged from acompressor is made to flow through both of first and second interiorheat exchangers. This allows for increasing the heating capacity insidethe vehicle cabin.

A second aspect of the present invention is an embodiment of the firstaspect of the present invention. In the second aspect,

the air-conditioning controller makes the heat pump device operate in ahot gas heating operation mode including a second hot gas heatingoperation mode in which the refrigerant discharged from the compressoris allowed to flow through the first interior heat exchanger, bypass thesecond interior heat exchanger, further bypass the exterior heatexchanger after pressure has been reduced by the pressure reducingvalve, and then be sucked into the compressor.

According to this configuration, if a high heating capacity needs to beachieved, the operation modes may be switched into the first hot gasheating operation mode. On the other hand, if the heating capacity maybe low, then the mode of operation may be the second hot gas heatingoperation mode. This thus allows for heating the vehicle cabin with thecapacity controlled depending on the situation.

A third aspect of the present invention is an embodiment of the secondaspect of the present invention. In the third aspect,

the vehicle air conditioner includes a degree-of-heating-requesteddetecting means for detecting the degree of heating requested.

The air-conditioning controller makes the heat pump device operate in afirst hot gas heating operation mode if the degree-of-heating-requesteddetecting means has found the degree of heating requested high, andmakes the heat pump device operate in a second hot gas heating operationmode if the degree-of-heating-requested detecting means has found thedegree of heating requested low.

This configuration allows for choosing an appropriate hot gas heatingoperation mode according to the degree of heating requested.

A fourth aspect of the present invention is an embodiment of the secondaspect of the present invention. In the fourth aspect,

the vehicle air conditioner includes a quality-of-wet-vapor detectingmeans for detecting the quality of wet vapor of the refrigerant suckedinto the compressor.

The air-conditioning controller makes a switch between the first andsecond hot gas heating operation modes in accordance with the quality ofwet vapor of the sucked refrigerant detected by the quality-of-wet-vapordetecting means.

According to this configuration, a switch is made between the first andsecond hot gas heating operation modes in accordance with the quality ofwet vapor of the sucked refrigerant. This prevents the compressor fromoperating in wet condition, thus increasing the reliability of the heatpump device.

A fifth aspect of the present invention is an embodiment of any one ofthe first to fourth aspects of the present invention. In the fifthaspect,

the heat pump device includes a refrigerant heater provided between thepressure reducing valve and the compressor.

If the decrease-in-quantity-of-heat-absorbed detecting means has sensedthat the quantity of heat absorbed by the exterior heat exchanger isequal to or smaller than a second predetermined value that is less thanthe first predetermined value, the air-conditioning controller activatesthe refrigerant heater to make the heat pump device operate in a hot gasheating operation mode.

According to this configuration, some heating capacity is ensured byactivating the refrigerant heater if the outside air temperature hasfurther decreased to the point that no heat can be absorbed at all fromthe outside air.

A sixth aspect of the present invention is an embodiment of any one ofthe first to fifth aspects of the present invention. In the sixthaspect,

the decrease-in-quantity-of-heat-absorbed detecting means is an outsideair temperature sensor that detects the temperature of air outside ofthe vehicle cabin.

This configuration allows for detecting a decrease in the quantity ofheat absorbed with reliability and at a low cost.

A seventh aspect of the present invention is an embodiment of any one ofthe first to fifth aspects of the present invention. In the seventhaspect,

the decrease-in-quantity-of-heat-absorbed detecting means is a frostingdetecting means for detecting a frosting condition of the exterior heatexchanger.

Specifically, if the exterior heat exchanger is frosted, the heatexchange efficiency decreases, so does the quantity of heat absorbedduring heating. According to the present invention, frosting in theexterior heat exchanger is detected, thereby determining whether or notthe quantity of heat absorbed has decreased. This allows for performinga control depending on the condition of the exterior heat exchanger.

An eighth aspect of the present invention is an embodiment of the fifthaspect of the present invention. In the eighth aspect,

the refrigerant heater is an electric heater that generates heat whensupplied with power from a battery mounted on the vehicle.

This configuration allows a vehicle air conditioner according to thepresent invention to be mounted and operated on an electric vehicle, forexample.

A ninth aspect of the present invention is an embodiment of the eighthaspect of the present invention. In the ninth aspect,

the vehicle air conditioner includes a battery level detecting means fordetecting a charge level of the battery.

If the charge level of the battery detected by the battery leveldetecting means is equal to or smaller than a predetermined value, theair-conditioning controller prohibits the refrigerant heater from beingactivated.

This configuration allows for cutting down the power to be dissipatedfor heating when the charge level of a battery is low.

A tenth aspect of the present invention is an embodiment of the eighthaspect of the present invention. In the tenth aspect,

the vehicle air conditioner includes a charging detecting means fordetermining whether the battery is being charged or not.

If the charging detecting means has sensed that the battery is now beingcharged, the air-conditioning controller activates the refrigerantheater.

This configuration allows for preparing to heat the vehicle cabin whilethe battery is being charged, i.e., before the vehicle starts to travel.In this case, the refrigerant heater is used to absorb heat into therefrigerant, thus ensuring some heating capacity for the vehicle thatstarts to travel when charged, without getting the exterior heatexchanger frosted. In addition, since the refrigerant heater isactivated during charging, the vehicle's distance to empty is notaffected.

An eleventh aspect of the present invention is an embodiment of thethird aspect of the present invention. In the eleventh aspect,

the interior air-conditioning unit includes an electric air heater, and

the air-conditioning controller determines whether or not an aircondition inside the vehicle cabin is going to reach a degree of heatingrequested detected by the degree-of-heating-requested detecting means,and activates the air heater if the controller has decided that thecondition will not reach the degree of heating requested.

According to this configuration, unless the degree of heating requestedis achieved even by performing a hot gas heating mode of operation, forexample, an electric air heater is activated, thus enabling compensationfor the heating capacity.

A twelfth aspect of the present invention is an embodiment of any one ofthe first to eleventh aspects of the present invention. In the twelfthaspect,

the air-conditioning controller makes the heat pump device operate inthe second hot gas heating operation mode at the beginning of heating.

According to this configuration, the mode of operation is set to be thesecond hot gas heating operation mode at the beginning of heating, whichallows for decreasing the overall volume of piping in one cycle andincreasing the amount of the refrigerant circulated. This results in anearly rise in pressure to a high level and an increase in quickness ofheating.

According to the first aspect of the present invention, if the quantityof heat absorbed by the exterior heat exchanger has decreased, theoperation modes are switched into a first hot gas heating operation modein which the refrigerant discharged from the compressor is allowed toflow through the first and second interior heat exchangers, bypass theexterior heat exchanger with pressure reduced, and then be sucked intothe compressor. This allows for reducing the overall consumption ofenergy for air conditioning while maintaining comfortableness of airconditioning not only in cooling but also in heating as well.

According to the second aspect of the present invention, if a highheating capacity needs to be achieved, the operation modes may beswitched into the first hot gas heating operation mode. On the otherhand, if the heating capacity may be low, then the mode of operation maybe the second hot gas heating operation mode. This thus allows forheating the vehicle cabin with the capacity controlled depending on thesituation.

According to the third aspect of the present invention, if the degree ofheating requested is high, the operation modes may be switched into thefirst hot gas heating operation mode. On the other hand, if the degreeof heating requested may be low, then the mode of operation may be thesecond hot gas heating operation mode. This thus allows for increasingcomfortableness in the vehicle cabin.

According to the fourth aspect of the present invention, a switch ismade between the first and second hot gas heating operation modes inaccordance with the quality of wet vapor of the refrigerant sucked intothe compressor. This prevents the compressor from operating in wetcondition, thus increasing the reliability of the heat pump device.

According to the fifth aspect of the present invention, if the quantityof heat absorbed by the exterior heat exchanger is even smaller, therefrigerant heater is activated to switch the modes into a hot gasheating operation mode. This thus ensures some heating capacity.

According to the sixth aspect of the present invention, a decrease inthe quantity of heat absorbed by the exterior heat exchanger is detectedby an outside air temperature sensor, thus allowing for detecting adecrease in the quantity of heat absorbed with reliability and at a lowcost.

According to the seventh aspect of the present invention, a decrease inthe quantity of heat absorbed by the exterior heat exchanger is detectedby a frosting detecting means of the exterior heat exchanger. Thisallows for performing a control depending on the condition of theexterior heat exchanger.

According to the eighth aspect of the present invention, the refrigerantheater is implemented as an electric heater, thus allowing a vehicle airconditioner according to the present invention to be mounted on anelectric vehicle, for example.

According to the ninth aspect of the present invention, the refrigerantheater is prohibited from being activated if the battery charge level ofa vehicle is low, thus allowing for increasing the distance to emptywhen a vehicle air conditioner according to the present invention ismounted on an electric vehicle.

According to the tenth aspect of the present invention, if the batteryis being charged, the refrigerant heater is activated, thus allowing forensuring some heating capacity before the vehicle starts to travel andafter the vehicle has traveled and increasing the occupant'scomfortableness. In addition, when the vehicle air conditioner ismounted on an electric vehicle, the distance to empty is hardlyaffected.

According to the eleventh aspect of the present invention, the airheater is activated if the decision has been made that the degree ofheating requested will not be reached even by performing a hot gasheating mode of operation. This thus allows for increasing theoccupant's comfortableness.

According to the twelfth aspect of the present invention, the operationmodes are switched into a second hot gas heating operation mode at thebeginning of heating, thus resulting in an increase in quickness ofheating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 generally illustrates a configuration for a vehicle airconditioner according to an embodiment.

FIG. 2 is a block diagram of a vehicle air conditioner.

FIG. 3 is a perspective view illustrating an upstream interior heatexchanger as viewed from an upstream side in an airflow direction.

FIG. 4 is a diagram corresponding to FIG. 1 and illustrating how the airconditioner operates in a cooling operation mode.

FIG. 5 is a diagram corresponding to FIG. 1 and illustrating how the airconditioner operates in a normal heating operation mode.

FIG. 6 is a diagram corresponding to FIG. 1 and illustrating how the airconditioner operates in a first hot gas heating operation mode.

FIG. 7 is a diagram corresponding to FIG. 1 and illustrating how the airconditioner operates in a second hot gas heating operation mode.

FIG. 8 is a diagram corresponding to FIG. 1 and illustrating how the airconditioner operates in a refrigerant-heated heating operation mode.

FIG. 9 is a diagram corresponding to FIG. 1 and illustrating how the airconditioner operates in a powerful defrosting operation mode.

FIG. 10 is a diagram corresponding to FIG. 1 and illustrating how theair conditioner operates in a moderate defrosting operation mode.

FIG. 11 is a diagram corresponding to FIG. 1 and illustrating how theair conditioner operates in a gentle defrosting operation mode.

FIG. 12 is a diagram corresponding to FIG. 1 and illustrating how theair conditioner operates in a first heating-dominant defrostingoperation mode.

FIG. 13 is a diagram corresponding to FIG. 1 and illustrating how theair conditioner operates in a second heating-dominant defrostingoperation mode.

FIG. 14 is flowchart showing how to perform a heating operationsubroutine control.

FIG. 15 is flowchart showing how to perform a defrosting operationsubroutine control.

FIG. 16 is a flowchart showing how to perform a control of selecting adefrosting operation mode according to the amount of frost deposited.

FIG. 17 illustrates a general configuration for a vehicle airconditioner as a variation.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings. Note that the followingdescription of preferred embodiments is only an example in nature and isnot intended to limit the scope, applications or use of the invention.

FIG. 1 generally illustrates a configuration for a vehicle airconditioner 1 according to an embodiment of the present invention. Avehicle on which the vehicle air conditioner 1 is mounted may be anelectric vehicle including a traction battery B (shown in FIG. 2) and atraction motor (not shown).

This vehicle air conditioner 1 includes a heat pump device 20, aninterior air-conditioning unit 21, and an air-conditioning controller 22(shown in FIG. 2) that controls the heat pump device 20 and the interiorair-conditioning unit 21.

The heat pump device 20 includes: a motor-driven compressor 30 thatcompresses a refrigerant; a downstream interior heat exchanger (firstinterior heat exchanger) 31 provided inside the vehicle cabin; anupstream interior heat exchanger (second interior heat exchanger) 32provided upstream of the downstream interior heat exchanger 31 in anairflow direction inside the vehicle cabin; an exterior heat exchanger33 provided outside the vehicle cabin; an accumulator 34; and first tofourth main refrigerant pipes 40 to 43, first to third branchrefrigerant pipes 44 to 46 and a bypass pipe BP which connect all ofthese members 30 to 34 together. The heat pump device 20 furtherincludes a refrigerant heater 35.

The motor-driven compressor 30 is an onboard compressor which has beenknown in the art, and is driven by an electric motor. The discharge rateper unit time is variable by changing the number of revolutions of themotor-driven compressor 30. The motor-driven compressor 30 is connectedto an air-conditioning controller 22 so as to have its ON/OFF statesswitched and its number of revolutions controlled. The motor-drivencompressor 30 is supplied with power from the traction battery B.

As shown in FIG. 3, the upstream interior heat exchanger 32 includes anupper header tank 47, a lower header tank 48, and a core 49. The core 49is obtained by alternately arranging horizontally (i.e., laterally inFIG. 3), and assembling together, vertically extending tubes 49 a andfins 49 b and is configured so that air-conditioning air passes betweenthose tubes 49 a. The flow direction of the air-conditioning air isindicated by the open arrow. Two rows of tubes 49 a are arranged in theflow direction of the outside air.

The respective upper ends of the tubes 49 a located upstream anddownstream in the airflow direction are both connected to the upperheader tank 47 so as to communicate with each other. Inside the upperheader tank 47, provided is a first partition 47 a which partitions theinside of the upper header tank 47 into an airflow upstream portion andan airflow downstream portion. The space located upstream of the firstpartition 47 a in the airflow direction communicates with the respectiveupper ends of the upstream tubes 49 a. On the other hand, the spacelocated downstream of the first partition 47 a in the airflow directioncommunicates with the respective upper ends of the downstream tubes 49a.

Inside the upper header tank 47, also provided is a second partition 47b which partitions the inside of the upper header tank 47 horizontally.A communication hole 47 e has been cut through a portion of the firstpartition 47 a which is located on the right-hand side of the secondpartition 47 b.

A refrigerant inlet 47 c has been cut through a portion of the left sidesurface of the upper header tank 47 downstream in the airflow direction,and a refrigerant outlet 47 d has been cut upstream in the airflowdirection.

Inside the lower header tank 48, also provided is a partition 48 a whichpartitions the inside of the lower header tank 48 into airflow upstreamand downstream portions, just like the first partition 47 a of the upperheader tank 47. The space located upstream of the partition 48 a in theairflow direction communicates with the respective lower ends of theupstream tubes 49 a, while the space located downstream of the partition48 a in the airflow direction communicates with the respective lowerends of the downstream tubes 49 a.

Having such a configuration, this upstream heat exchanger 32 has fourpaths in total. Specifically, first of all, a refrigerant flowing inthrough the inlet 47 c enters a room R1 which is located downstream ofthe first partition 47 a of the upper header tank 47 in the airflowdirection and on the left hand side of the second partition 47 b. Then,the refrigerant flows downward through the tubes 49 a communicating withthis room R1.

Thereafter, the refrigerant enters the space 51 of the lower header tank48 which is located downstream of the partition 48 a in the airflowdirection, flows to the right, and then flows upward through the tubes49 a. Then, the refrigerant enters the room R2 of the upper header tank47 located downstream of the first partition 47 a in the airflowdirection and on the right hand side of the second partition 47 b.

Subsequently, the refrigerant in the room R2 passes through thecommunication hole 47 e of the first partition 47 a, enters the room R3of the upper header tank 47 located upstream of the first partition 47 ain the airflow direction and on the right hand side of the secondpartition 47 b, and then flows downward through the tubes 49 acommunicating with the room R3.

After that, the refrigerant enters the space S2 of the lower header tank48 located upstream of the partition 48 a in the airflow direction,flows to the left, and then flows upward through the tubes 49 a.Thereafter, the refrigerant enters the room R4 of the upper header tank47 located upstream of the first partition 47 a in the airflow directionand on the left hand side of the second partition 47 b, and then flowsout through the outlet 47 d.

In the upstream interior heat exchanger 32, a windward path P1 isconstituted by the path upstream in the airflow direction, and a leewardpath P2 is constituted by the path downstream in the airflow direction.

The downstream interior heat exchanger 31 just has a smaller size than,but has the same or similar structure as/to, the upstream interior heatexchanger 32, and a detailed description thereof will be omitted herein.Optionally, the downstream and upstream interior heat exchangers 31 and32 may have different structures.

The exterior heat exchanger 33 is provided near the front end of a motorroom (corresponding to the engine room of an engine-driven vehicle) in afront portion of a vehicle, and is configured to catch the wind blowingagainst the vehicle traveling. Although not shown, the exterior heatexchanger 33 also includes an upper header tank, a lower header tank anda core. The core includes a tube that extends vertically.

As shown in FIG. 1, a cooling fan 37 is provided for the vehicle. Thiscooling fan 37 is driven by a fan motor 38, and is configured to blowair to the exterior heat exchanger 33. The fan motor 38 is connected tothe air-conditioning controller 22 to have its ON/OFF states switchedand its number of revolutions controlled. The fan motor 38 is alsosupplied with electric power from the traction battery B. Note that thecooling fan 37 may also blow air to a radiator that cools a tractioninverter, for example, and may also be activated even if airconditioning is not requested.

The accumulator 34 is provided near the suction port of the motor-drivencompressor 30 and halfway along the fourth main refrigerant pipe 43.

On the other hand, the first main refrigerant pipe 40 connects togetherthe discharge port of the motor-driven compressor 30 and the refrigerantinlet of the downstream interior heat exchanger 31. Moreover, the secondmain refrigerant pipe 41 connects together the refrigerant outlet of thedownstream interior heat exchanger 31 and the refrigerant inlet of theexterior heat exchanger 33. The third main refrigerant pipe 42 connectstogether the refrigerant outlet of the exterior heat exchanger 33 andthe refrigerant inlet of the upstream interior heat exchanger 32. Thefourth main refrigerant pipe 43 connects together the refrigerant outletof the upstream interior heat exchanger 32 and the suction port of themotor-driven compressor 30.

The first branch refrigerant pipe 44 branches from the second mainrefrigerant pipe 41, and is connected to the third main refrigerant pipe42. The second branch refrigerant pipe 45 branches from the second mainrefrigerant pipe 41, and is connected to the fourth main refrigerantpipe 43. The third branch refrigerant pipe 46 branches from the thirdmain refrigerant pipe 42, and is connected to the fourth mainrefrigerant pipe 43.

The bypass pipe BP is a pipe which makes the refrigerant flowing throughthe second main refrigerant pipe 41 bypass the exterior heat exchanger33 and flow through the third main refrigerant pipe 42. The bypass pipeBP is connected to a point on the second main refrigerant pipe 41upstream of the exterior heat exchanger 33 and also connected to a pointon the third main refrigerant pipe 42 downstream of the exterior heatexchanger 33.

The heat pump device 20 further includes a first flow path switchingvalve 50, a second flow path switching valve 51, a first pressurereducing valve 52, a second pressure reducing valve 53, a first checkvalve 54, a second check valve 55 and a bypass switching valve 56.

The first flow path switching valve 50, the second flow path switchingvalve 51 and the bypass switching valve 56 are configured as electricthree-way valves, and are controlled by the air-conditioning controller22. The first flow path switching valve 50 is provided halfway along thesecond main refrigerant pipe 41, and the first branch refrigerant pipe44 is connected to the valve 50. The second flow path switching valve 51is provided halfway along the fourth main refrigerant pipe 43, and thethird branch refrigerant pipe 46 is connected to the valve 51. Thebypass switching valve 56 is provided halfway along the second mainrefrigerant pipe 41 and downstream of the first flow path switchingvalve 50 in the refrigerant flow direction and an upstream side of thebypass pipe BP is connected to the bypass switching valve 56. By beingswitched by the air-conditioning controller 22, the bypass switchingvalve 56 allows the refrigerant flowing through the second mainrefrigerant pipe 41 to pass through only the exterior heat exchanger 33,only the bypass pipe BP, or both the exterior heat exchanger 33 and thebypass pipe BP selectively. The flow rate ratio of the refrigerantsflowing through the exterior heat exchanger 33 and the bypass pipe BP ischangeable arbitrarily.

The first and second pressure reducing valves 52 and 53 are electrictypes to be controlled by the air-conditioning controller 22 to operatein either a closing direction in which the valves exhibit a pressurereducing action or in an opening direction in which the valves exhibitno pressure reducing action. The degrees of opening of the first andsecond pressure reducing valves 52 and 53 are ordinarily set accordingto the condition of the air-conditioning load, but may also be set to bean arbitrary degree irrespective of the air-conditioning load.

The first pressure reducing valve 52 is provided closer to the upstreaminterior heat exchanger 32 than the point of connection between thethird main refrigerant pipe 42 and the first branch refrigerant pipe 44is, i.e., provided on a refrigerant pipe leading to the refrigerantinlet of the upstream interior heat exchanger 32. On the other hand, thesecond pressure reducing valve 53 is provided on the second mainrefrigerant pipe 41 between the first flow path switching valve 50 andthe bypass switching valve 56. That is to say, the second pressurereducing valve 53 is arranged on the second main refrigerant pipe 41between the point of connection with the bypass pipe BP and thedownstream interior heat exchanger 31.

The first check valve 54 is provided on the third main refrigerant pipe42, and is configured to allow the refrigerant to flow through the thirdmain refrigerant pipe 42 from the exterior heat exchanger 33 toward theupstream interior heat exchanger 32 and to prevent the refrigerant fromflowing in the reverse direction.

The second check valve 55 is provided on the second branch refrigerantpipe 45, and is configured to allow the refrigerant to flow through thesecond branch refrigerant pipe 45 from the fourth main refrigerant pipe43 toward the second main refrigerant pipe 41 and to prevent therefrigerant from flowing in the reverse direction.

The refrigerant heater 35 is arranged on the second main refrigerantpipe 41 between the second pressure reducing valve 53 and the bypassswitching valve 56, i.e., between the second pressure reducing valve 53and the motor-driven compressor 30. The refrigerant heater 35 isconfigured as an electric heater that heats the refrigerant flowingthrough the second main refrigerant pipe 41, and has its ON/OFF statesswitched, and the degree of heating adjusted, by the air-conditioningcontroller 22. The refrigerant heater 35 is also supplied with electricpower from the traction battery B.

The interior air-conditioning unit 21 further includes a casing 60housing the downstream and upstream interior heat exchangers 31 and 32,an air mix door (temperature controlling door) 62, an air mix dooractuator 63 that drives the air mix door 62, blowout-mode switchingdoors 64, a blower 65, and a PTC heater (electric air heater) 67.

The blower 65 is provided to select one of the air inside the vehiclecabin (inside air) or the air outside the vehicle cabin (outside air)and blow the selected air as air-conditioning air into the casing 60.The blower 65 includes a sirocco fan 65 a and a blower motor 65 b thatdrives the sirocco fan 65 a in rotation. The blower motor 65 b isconnected to the air-conditioning controller 22 to have its ON/OFFstates switched and its number of revolutions controlled. The blowermotor 65 b is also supplied with electric power from the tractionbattery B.

The blower 65 is provided with an inside air inlet port 65 c tointroduce the inside air and an outside air inlet port 65 d to introducethe outside air. Inside the blower 65, provided is an inside/outside airswitching door 65 e to open one of the inside and outside air inletports 65 c and 65 d and close the other. The blower 65 is furtherprovided with an inside/outside air switching door actuator 61 to drivethe inside/outside air switching door 65 e. This inside/outside airswitching door actuator 61 is controlled by the air-conditioningcontroller 22. The blower 65 is configured to have its air introducingmodes switched between an inside air introducing mode in which theinside air inlet port 65 c is fully opened and the outside air inletport 65 d is fully closed and an outside air introducing mode in whichthe inside air inlet port 65 c is fully closed and the outside air inletport 65 d is fully opened. The blower 65 is configured so as to allowthe occupant to select either one of the inside and outside airintroducing modes by turning a switch. However, the blower 65 is alsoconfigured so that the air-conditioning controller 22 automaticallyswitches the modes under a predetermined condition.

The casing 60 is provided inside an instrument panel (not shown) in thevehicle cabin. The casing 60 has a defroster outlet port 60 a, a ventoutlet port 60 b, and a heat outlet port 60 c. The defroster outlet port60 a is provided to supply the air-conditioning air to the inner surfaceof the windshield in the vehicle cabin. The vent outlet port 60 b isprovided to supply the air-conditioning air to (mainly the upper bodyof) the occupant in the vehicle cabin. The heat outlet port 60 c isprovided to supply the air-conditioning air to the feet of the occupantin the cabin.

These outlet ports 60 a-60 c are each opened and closed by an associatedone of the blowout-mode switching doors 64. Although not shown, theblowout-mode switching doors 64 are operated by an actuator connected tothe air-conditioning controller 22.

Examples of the blowout modes include a defroster blowout mode in whichthe air-conditioning air is supplied to the defroster outlet port 60 a,a vent blowout mode in which the air-conditioning air is supplied to thevent outlet port 60 b, a heat blowout mode in which the air-conditioningair is supplied to the heat outlet port 60 c, a defroster/heat mode inwhich the air-conditioning air is supplied to the defroster outlet port60 a and the heat outlet port 60 c, and a bi-level mode in which theair-conditioning air is supplied to the vent outlet port 60 b and theheat outlet port 60 c.

All of the air-conditioning air introduced into the casing 60 passesthrough the upstream interior heat exchanger 32.

In the casing 60, the air mix door 62 is provided between the upstreamand downstream interior heat exchangers 32 and 31. The air mix door 62is configured to control the temperature of the air-conditioning airsuch that the air that has passed through the upstream interior heatexchanger 32 which is going to pass through the downstream interior heatexchanger 31 is changed to determine a mixing ratio between the air thathas passed through the upstream interior heat exchanger 32 and the airthat has passed through the downstream interior heat exchanger 31.

The PTC heater 67 is arranged downstream of the downstream interior heatexchanger 33 in the airflow direction inside the casing 60 in order toheat the air-conditioning air flowing inside the casing 60. The PTCheater 67 is controlled by the air-conditioning controller 22 so as tohave its ON/OFF states switched and have the degree of heating changed.The PTC heater 67 is supplied with electric power from the tractionbattery B.

The vehicle air conditioner 1 further includes an outside airtemperature sensor 70, an exterior heat exchanger temperature sensor 71,an interior heat exchanger temperature sensor 73, an inside airtemperature sensor 75, a quality-of-wet-vapor detecting sensor(quality-of-wet-vapor detecting means) 80, a battery level detectingsensor 81 (shown in FIG. 2), and a charging state detecting sensor 82(shown in FIG. 2). These sensors are connected to the air-conditioningcontroller 22.

The outside air temperature sensor 70 is provided upstream of theexterior heat exchanger 33 in the airflow direction in order to detectthe temperature of the outside air (outside air temperature TG) that hasnot entered the exterior heat exchanger 33 yet. On the other hand, theexterior heat exchanger temperature sensor 71 is arranged on a surfaceof the exterior heat exchanger 33 which is located downstream in theairflow direction in order to detect the surface temperature of theexterior heat exchanger 33.

The interior heat exchanger temperature sensor 73 is provided downstreamof the upstream interior heat exchanger 32 in the airflow direction inorder to detect the surface temperature of the upstream interior heatexchanger 32. Based on the temperature of the upstream interior heatexchanger 32 detected downstream in the airflow direction by theinterior heat exchanger temperature sensor 73, a determination may bemade whether or not frost has been deposited in the upstream interiorheat exchanger 32.

The inside air temperature sensor 75 is provided to detect thetemperature inside the vehicle cabin (the inside air temperature TR) andis arranged at a predetermined position inside the vehicle cabin. Theinside air temperature sensor 75 is a sensor that has been known in theart, and a detailed description thereof will be omitted herein.

The quality-of-wet-vapor detecting sensor 80 is a sensor for detectingthe quality of wet vapor of the refrigerant to be sucked into themotor-driven compressor 30, and is configured to detect the quality ofwet vapor based on the pressure and temperature of the refrigerant nearthe refrigerant outlet of the exterior heat exchanger 33.

The battery level detecting sensor 81 is equivalent to a battery leveldetecting means according to the present invention, and has the abilityto detect the level of the traction battery B. The battery leveldetecting sensor 81 may be a known one.

The charging state detecting sensor 82 is equivalent to a chargingdetecting means according to the present invention, and has the abilityto determine whether or not the traction battery B is being charged byan external power supply. The “external power supply” refers herein toany power supply other than the vehicle's power generator, and may be ahousehold wall outlet or parking lot charging equipment, for example.This charging state detecting sensor 82 may also be a known one.

Although not shown, the vehicle air conditioner 1 also includes a solarradiation sensor and other kinds of sensors.

The air-conditioning controller 22 is configured to control the heatpump device 20 and other components by reference to multiple pieces ofinformation including the temperature set by the occupant, the outsideair temperature, the temperature inside the vehicle cabin, and theintensity of solar radiation. The air-conditioning controller 22 may beimplemented as a well-known central processing unit, ROM, or RAM, forexample. In addition, the air-conditioning controller 22 furthercontrols the motor-driven compressor 30 and the fan motor 38 dependingon the air-conditioning load.

As in an ordinary automatic air conditioning control, theair-conditioning controller 22 controls, through a main routine to bedescribed later, a switch of the operation modes of the heat pump device20, the volume of the air to be blown by the blower 65, the degree ofopening of the air mix door 62, a switch of the blowout modes, themotor-driven compressor 30, and the blower motor 65 b. For example,although the fan motor 38 is basically activated while the motor-drivencompressor 30 is activated, the fan motor 38 also is activated even ifthe motor-driven compressor 30 is at a stop, e.g., when the tractioninverter needs to be cooled.

The operation modes of the heat pump device 20 include: a coolingoperation mode; a normal heating operation mode; a first hot gas heatingoperation mode; a second hot gas heating operation mode; arefrigerant-heated heating operation mode; a powerful defrostingoperation mode; a moderate defrosting operation mode; a gentledefrosting operation mode; a first heating-dominant defrosting operationmode; and a second heating-dominant defrosting operation mode.

The cooling operation mode shown in FIG. 4 is selected when the outsideair temperature is higher than 25° C., for example. In the coolingoperation mode, the downstream interior heat exchanger 31 is made tofunction as a radiator, the upstream interior heat exchanger 32 is madeto function as a heat absorber, and the exterior heat exchanger 33 ismade to function as a radiator.

Specifically, the first flow path switching valve 50 switches the flowpaths such that a refrigerant that has flowed out of the downstreaminterior heat exchanger 31 does not flow into the upstream interior heatexchanger 32 through the inlet thereof but flows toward the secondpressure reducing valve 53. On the other hand, the second flow pathswitching valve 51 switches the flow paths such that the refrigerantthat has flowed out of the upstream interior heat exchanger 32 flowsinto the accumulator 34. The bypass switching valve 56 switches the flowpaths such that the refrigerant flowing through the second mainrefrigerant pipe 41 flows through only the exterior heat exchanger 33.The first pressure reducing valve 52 is turned into the expansion state,and the second pressure reducing valve 53 is turned into thenon-expansion state.

If the motor-driven compressor 30 is activated in this state, thehigh-pressure refrigerant discharged from the motor-driven compressor 30flows into the downstream interior heat exchanger 31 through the firstmain refrigerant pipe 40, and circulates through the downstream interiorheat exchanger 31. The refrigerant that has circulated through thedownstream interior heat exchanger 31 flows, without expanding, into theexterior heat exchanger 33 through the second main refrigerant pipe 41.The refrigerant that has flowed into the exterior heat exchanger 33dissipates heat, and expands by passing through the first pressurereducing valve 52 via the third main refrigerant pipe 42. Then, therefrigerant flows into the upstream interior heat exchanger 32. Therefrigerant that has flowed into the upstream interior heat exchanger 32circulates through the upstream interior heat exchanger 32 to absorbheat from the air-conditioning air. The refrigerant that has circulatedthrough the upstream interior heat exchanger 32 passes through thefourth main refrigerant pipe 43 and is sucked into the motor-drivencompressor 30 via the accumulator 34.

The normal heating operation mode shown in FIG. 5 is selected when theoutside air temperature is lower than 0° C. (at an extremely-low outsideair temperature), for example. In the normal heating operation mode, thedownstream and upstream interior heat exchangers 31 and 32 are made tofunction as radiators, and the exterior heat exchanger 33 is made tofunction as a heat absorber.

Specifically, the first flow path switching valve 50 switches the flowpaths such that the refrigerant that has flowed out of the downstreaminterior heat exchanger 31 flows into the upstream interior heatexchanger 32 through the inlet thereof. Meanwhile, the second flow pathswitching valve 51 switches the flow paths such that the refrigerantthat has flowed out of the exterior heat exchanger 33 flows into theaccumulator 34. The bypass switching valve 56 switches the flow pathssuch that the refrigerant flowing through the second main refrigerantpipe 41 flows through only the exterior heat exchanger 33. The firstpressure reducing valve 52 is turned into the non-expansion state, andthe second pressure reducing valve 53 is turned into the expansionstate.

If the motor-driven compressor 30 is activated in this state, thehigh-pressure refrigerant discharged from the motor-driven compressor 30flows into the downstream interior heat exchanger 31 through the firstmain refrigerant pipe 40, and circulates through the downstream interiorheat exchanger 31. The refrigerant that has circulated through thedownstream interior heat exchanger 31 flows through the second mainrefrigerant pipe 41 into the upstream interior heat exchanger 32 via thefirst branch refrigerant pipe 44. Then, the refrigerant circulatesthrough the upstream interior heat exchanger 32. That is, since thehigh-temperature refrigerant flows into the downstream and upstreaminterior heat exchangers 31 and 32, the air-conditioning air is heatedby both of the downstream and upstream interior heat exchangers 31 and32. As a result, a high heating capacity is achieved.

The refrigerant that has circulated through the upstream interior heatexchanger 32 flows through the fourth main refrigerant pipe 43 into thesecond main refrigerant pipe 41 via the second branch refrigerant pipe45. The refrigerant flowing into the second main refrigerant pipe 41expands by passing through the second pressure reducing valve 53, andthen flows into the exterior heat exchanger 33. The refrigerant that hasflowed into the exterior heat exchanger 33 absorbs heat from the outsideair. Then, the refrigerant passes through the third main refrigerantpipe 42 and the third branch refrigerant pipe 46 in this order, and issucked into the motor-driven compressor 30 by way of the accumulator 34.

The first hot gas heating operation mode shown in FIG. 6 is selectedwhen it is difficult to absorb heat using the exterior heat exchanger33. In the first hot gas heating operation mode, the downstream andupstream interior heat exchangers 31 and 32 are made to function asradiators. Also, the refrigerant is allowed to flow while bypassing theexterior heat exchanger 33.

Specifically, the first and second flow path switching valves 50 and 51and the first and second pressure reducing valves 52 and 53 aremaintained in the same state as in the normal heating mode. The bypassswitching valve 56 switches the flow paths so that the refrigerantflowing through the second main refrigerant pipe 41 flows through onlythe bypass pipe BP.

If the motor-driven compressor 30 is activated in this state, thehigh-pressure refrigerant discharged from the motor-driven compressor 30flows into the downstream interior heat exchanger 31 through the firstmain refrigerant pipe 40, and circulates through the downstream interiorheat exchanger 31. The refrigerant that has circulated through thedownstream interior heat exchanger 31 flows through the second mainrefrigerant pipe 41 into the upstream interior heat exchanger 32 via thefirst branch refrigerant pipe 44. Then, the refrigerant circulatesthrough the upstream interior heat exchanger 32. That is, since therefrigerant discharged from the motor-driven compressor 30 flows intothe downstream and upstream interior heat exchangers 31 and 32, theair-conditioning air is heated by both of the downstream and upstreaminterior heat exchangers 31 and 32.

The refrigerant that has circulated through the upstream interior heatexchanger 32 flows through the fourth main refrigerant pipe 43 into thesecond main refrigerant pipe 41 via the second branch refrigerant pipe45. The refrigerant that has flowed into the second main refrigerantpipe 41 expands by passing through the second pressure reducing valve53, flows through the bypass pipe BP, passes through the third mainrefrigerant pipe 42 and the third branch refrigerant pipe 46 in thisorder, and then is sucked into the motor-driven compressor 30 by way ofthe accumulator 34. In this first hot gas heating operation mode, therefrigerant flows while bypassing the exterior heat exchanger 33.

The second hot gas heating operation mode shown in FIG. 7 is selectedwhen it is difficult to absorb heat using the exterior heat exchanger 33and when the heating capacity may be lower than in the first hot gasheating operation mode shown in FIG. 6. In the second hot gas heatingoperation mode, the downstream interior heat exchanger 31 is made tofunction as a radiator. Also, the refrigerant is allowed to flow whilebypassing the exterior heat exchanger 33 and the upstream interior heatexchanger 32.

Specifically, the first flow path switching valve 50 switches the flowpaths so as to prevent the refrigerant that has flowed out of thedownstream interior heat exchanger 31 from flowing into the upstreaminterior heat exchanger 32 through its inlet and allow the refrigerantto flow toward the second pressure reducing valve 53. The second flowpath switching valve 51 and the second pressure reducing valve 53 aremaintained in the same state as in the normal heating operation mode.The bypass switching valve 56 switches the flow paths so that therefrigerant flowing through the second main refrigerant pipe 41 flowsthrough only the bypass pipe BP.

If the motor-driven compressor 30 is activated in this state, thehigh-pressure refrigerant discharged from the motor-driven compressor 30flows into the downstream interior heat exchanger 31 through the firstmain refrigerant pipe 40, and circulates through the downstream interiorheat exchanger 31. The refrigerant that has circulated through thedownstream interior heat exchanger 31 flows into the second mainrefrigerant pipe 41. The refrigerant that has flowed into the secondmain refrigerant pipe 41 expands by passing through the second pressurereducing valve 53, flows through the bypass pipe BP, passes through thethird main refrigerant pipe 42 and the third branch refrigerant pipe 46in this order, and then is sucked into the motor-driven compressor 30 byway of the accumulator 34. In this mode, the refrigerant discharged fromthe motor-driven compressor 30 does not flow through the upstreaminterior heat exchanger 32, and therefore, the heating capacity becomeslower than in the first hot gas heating operation mode shown in FIG. 6.

The refrigerant-heated heating operation mode shown in FIG. 8 isselected when it is even more difficult to absorb heat using theexterior heat exchanger 33 (i.e., when it is virtually impossible toabsorb heat from the outside air). In the refrigerant-heated heatingoperation mode, the downstream and upstream interior heat exchangers 31and 32 are made to function as radiators. Also, the refrigerant isallowed to flow while bypassing the exterior heat exchanger 33, and therefrigerant heater 35 is turned ON.

Specifically, the first and second flow path switching valves 50 and 51,the first and second pressure reducing valves 52 and 53, and the bypassswitching valve 56 are maintained in the same state as in the first hotgas heating operation mode.

If the motor-driven compressor 30 is activated in this state, therefrigerant discharged from the motor-driven compressor 30 circulatesthrough the downstream interior heat exchanger 31 and the upstreaminterior heat exchanger 32 in this order, passes through the fourth mainrefrigerant pipe 43 and the second branch refrigerant pipe 45 and flowsinto the second main refrigerant pipe 41. The refrigerant that hasflowed into the second main refrigerant pipe 41 expands by passingthrough the second pressure reducing valve 53 and then is heated by therefrigerant heater 35. Thereafter, the refrigerant flows through thebypass pipe BP, passes through the third main refrigerant pipe 42 andthe third branch refrigerant pipe 46 in this order, and then is suckedinto the motor-driven compressor 30 via the accumulator 34.

The powerful defrosting operation mode shown in FIG. 9 is selected inorder to melt frost deposited, if any, in the exterior heat exchanger 33during heating. In the powerful defrosting operation mode, thedownstream interior heat exchanger 31 and the exterior heat exchanger 33are made to function as radiators, and the refrigerant is allowed toflow while bypassing the upstream interior heat exchanger 32.

Specifically, the first flow path switching valve 50 switches the flowpaths so as to prevent the refrigerant that has flowed out of thedownstream interior heat exchanger 31 from flowing into the upstreaminterior heat exchanger 32 through its inlet and to allow therefrigerant to flow toward the second pressure reducing valve 53.Meanwhile, the second flow path switching valve 51 switches the flowpaths so as to allow the refrigerant that has flowed out of the exteriorheat exchanger 33 to flow into the accumulator 34. The bypass switchingvalve 56 switches the flow paths so that the refrigerant flowing throughthe second main refrigerant pipe 41 flows through only the exterior heatexchanger 33. The second pressure reducing valve 53 is turned into thenon-expansion state.

If the motor-driven compressor 30 is activated in this state, therefrigerant discharged from the motor-driven compressor 30 circulatesthrough the downstream interior heat exchanger 31, and then flows intothe exterior heat exchanger 33 without expanding by passing through thesecond main refrigerant pipe 41. The refrigerant that has flowed intothe exterior heat exchanger 33 dissipates heat to melt the frost there.Thereafter, the refrigerant passes through the third main refrigerantpipe 42 and the third branch refrigerant pipe 46 in this order and thenis sucked into the motor-driven compressor 30 via the accumulator 34.

The moderate defrosting operation mode shown in FIG. 10 is selected inorder to melt frost deposited, if any, in the exterior heat exchanger 33during heating, and has its defrosting capacity set to be lower than inthe powerful defrosting operation mode shown in FIG. 9. In the moderatedefrosting operation mode, the downstream interior heat exchanger 31 andthe exterior heat exchanger 33 are made to function as radiators, andpart of the refrigerant is allowed to flow through the bypass pipe BP.Also, the refrigerant is made to bypass the upstream interior heatexchanger 32.

Specifically, the first and second flow path switching valves 50 and 51and the first and second pressure reducing valves 52 and 53 aremaintained in the same state as in the powerful defrosting operationmode. The bypass switching valve 56 switches the flow paths such thatthe refrigerant flowing through the second main refrigerant pipe 41flows through both of the exterior heat exchanger 33 and the bypass pipeBP.

If the motor-driven compressor 30 is activated in this state, therefrigerant discharged from the motor-driven compressor 30 circulatesthrough the downstream interior heat exchanger 31, and then flows intothe exterior heat exchanger 33 and the bypass pipe BP without expandingby passing through the second main refrigerant pipe 41. The refrigerantthat has flowed into the exterior heat exchanger 33 dissipates heat tomelt the frost there, while the refrigerant that has flowed into thebypass pipe BP flows into the third main refrigerant pipe 42 almostwithout dissipating heat. The refrigerant that has flowed into theexterior heat exchanger 33 and the refrigerant that has flowed throughthe bypass pipe BP are confluent with each other in the third mainrefrigerant pipe 42. The confluent refrigerant passes through the thirdbranch refrigerant pipe 46 and then is sucked into the motor-drivencompressor 30 via the accumulator 34. Since some of the refrigerantflowing through the second main refrigerant pipe 41 flows through thebypass pipe BP, the defrosting capacity becomes lower than in thepowerful defrosting operation mode.

The gentle defrosting operation mode shown in FIG. 11 is selected inorder to melt frost deposited, if any, in the exterior heat exchanger 33while a heating operation is being performed when the outside airtemperature is relatively high (e.g., higher than 0° C.), and has itsdefrosting capacity set to be lower than in the moderate defrostingoperation mode shown in FIG. 10. In the gentle defrosting operationmode, the downstream and upstream interior heat exchanger 31 and 32 aremade to function as radiators, and the refrigerant is made to bypass theexterior heat exchanger 33.

Specifically, the first and second flow path switching valves 50 and 51,the first and second pressure reducing valves 52 and 53, and the bypassswitching valve 56 are maintained in the same state as in the first hotgas heating operation mode.

If the motor-driven compressor 30 is activated in this state, thehigh-pressure refrigerant discharged from the motor-driven compressor 30circulates through the downstream and upstream interior heat exchangers31 and 32 in this order. The air-conditioning air is heated by both ofthe downstream and upstream interior heat exchangers 31 and 32. Thus,the heating capacity becomes higher in this mode than in the powerfuldefrosting operation mode and the moderate defrosting operation mode.

The refrigerant that has circulated through the upstream interior heatexchanger 32 passes through the fourth main refrigerant pipe 43 and thesecond branch refrigerant pipe 45 and flows into the second mainrefrigerant pipe 41. The refrigerant that has flowed into the secondmain refrigerant pipe 41 expands by passing through the second pressurereducing valve 53, flows through the bypass pipe BP, passes through thethird main refrigerant pipe 42 and the third branch refrigerant pipe 46in this order, and then is sucked into the motor-driven compressor 30via the accumulator 34. Although no refrigerant flows through theexterior heat exchanger 33, the frost still melts by absorbing heat fromthe wind blowing against the vehicle traveling and from the surroundingair, because this gentle defrosting operation mode is selected when theoutside air temperature is relatively high.

The first heating-dominant defrosting operation mode shown in FIG. 12 isselected in order to melt frost deposited, if any, in the exterior heatexchanger 33 during heating while performing a heating operation with atleast a predetermined capacity. In the first heating-dominant defrostingoperation mode, the downstream and upstream interior heat exchangers 31and 32 and the exterior heat exchanger 33 are all made to function asradiators.

Specifically, the first and second flow path switching valves 50 and 51,the first pressure reducing valve 52, and the bypass switching valve 56are maintained in the same state as in the normal heating operationmode. The second pressure reducing valve 53 is turned into thenon-expansion state.

If the motor-driven compressor 30 is activated in this state, thehigh-pressure refrigerant discharged from the motor-driven compressor 30circulates through the downstream and upstream interior heat exchangers31 and 32 in this order. The air-conditioning air is heated by both ofthe downstream and upstream interior heat exchangers 31 and 32. Thus,the heating capacity increases.

The refrigerant that has circulated through the upstream interior heatexchanger 32 passes through the fourth main refrigerant pipe 43 and thesecond branch refrigerant pipe 45 to flow into the second mainrefrigerant pipe 41. The refrigerant that has flowed into the secondmain refrigerant pipe 41 flows into the exterior heat exchanger 33without expanding. Thus, the frost deposited in the exterior heatexchanger 33 melts.

The second heating-dominant defrosting operation mode shown in FIG. 13is selected in order to melt frost deposited, if any, in the exteriorheat exchanger 33 during heating while performing a heating operationwith at least a predetermined capacity. The heating capacity is set tobe lower in this mode than in the first heating-dominant defrostingoperation mode. In the second heating-dominant defrosting operationmode, the downstream and upstream interior heat exchangers 31 and 32 andthe exterior heat exchanger 33 are all made to function as radiators,and some of the refrigerant flowing through the second main refrigerantpipe 41 is made to flow through the bypass pipe BP.

Specifically, the first and second flow path switching valves 50 and 51,and the first and second pressure reducing valves 52 and 53 aremaintained in the same state as in the first heating-dominant defrostingoperation mode. The bypass switching valve 56 switches the flow pathssuch that the refrigerant flowing through the second main refrigerantpipe 41 passes through both of the exterior heat exchanger 33 and thebypass pipe BP.

If the motor-driven compressor 30 is activated in this state, thehigh-pressure refrigerant discharged from the motor-driven compressor 30circulates through the downstream and upstream interior heat exchangers31 and 32 in this order. The air-conditioning air is heated by both ofthe downstream and upstream interior heat exchangers 31 and 32.

The refrigerant that has circulated through the upstream interior heatexchanger 32 passes through the fourth main refrigerant pipe 43 and thesecond branch refrigerant pipe 45 to flow into the second mainrefrigerant pipe 41. The refrigerant that has flowed into the secondmain refrigerant pipe 41 flows into the exterior heat exchanger 33 andthe bypass pipe BP without expanding. Thus, the frost is melted by therefrigerant that has flowed into the exterior heat exchanger 33. Sincenot all of the refrigerant is allowed to flow through the exterior heatexchanger 33, the heating capacity becomes higher than in the firstheating-dominant defrosting operation mode.

As shown in FIG. 2, the air-conditioning controller 22 includes afrosting detecting section (frosting detecting means) 22 a whichdetermines whether or not frost has been deposited in the exterior heatexchanger 33 and how much frost has been deposited there, if any. Thefrosting detecting section 22 a decides that frost has been depositedthere if a value obtained by subtracting the surface temperature of theexterior heat exchanger 33 detected by the exterior heat exchangertemperature sensor 71 from the outside air temperature (TG) detected bythe outside air temperature sensor 70 is greater than, e.g., 20 (° C.).That is, frosting is detected based on the fact that if frost has beendeposited in the exterior heat exchanger 33, the refrigerant cannotabsorb heat in the exterior heat exchanger 33 and its temperature doesnot rise. Thus, the value of “20” may be changed into any other value aslong as a determination can be made, based on that value, whether or notfrost has been deposited in the exterior heat exchanger 33.Alternatively, deposition of frost may be detected directly. Meanwhile,the amount of frost deposited may be detected based on the differencebetween the outside air temperature (TG) detected by the outside airtemperature sensor 70 and the temperature detected by the exterior heatexchanger temperature sensor 71. The greater the difference betweenthese temperatures, the larger the amount of frost deposited is regardedto be.

The frosting detecting section 22 a also functions as adecrease-in-quantity-of-heat-absorbed detecting means for determiningwhether or not the quantity of heat absorbed by the exterior heatexchanger 33 has decreased during heating. As described above, if frostis deposited in the exterior heat exchanger 33, the quantity of heatabsorbed from the outside air decreases. However, since there is acorrelation between the amount of frost deposited and such a decrease inthe quantity of heat absorbed, the decrease in the quantity of heatabsorbed by the exterior heat exchanger 33 may be detected by thefrosting detecting section 22 a. That is to say, the magnitude of thedecrease in the quantity of heat absorbed by the exterior heat exchanger33 may be detected based on the amount of frost deposited in theexterior heat exchanger 33.

In this embodiment, the frosting detecting section 22 a is configured todetermine whether or not the amount of frost deposited in the exteriorheat exchanger 33 is equal to or smaller than a first predeterminedvalue and whether the amount of frost deposited there is equal to orsmaller than a second predetermined value that is less than the firstpredetermined value. The first predetermined value is set to be such avalue at which it is too difficult to absorb heat using the exteriorheat exchanger to avoid a significant decline in heating capacity. Onthe other hand, the second predetermined value is set to be such a valueat which it is almost impossible to absorb heat using the exterior heatexchanger 33 and no heating operation can be performed.

The magnitude of decrease in the quantity of heat absorbed by theexterior heat exchanger 33 may be detected either by the frostingdetecting section 22 a described above or based on an outside airtemperature sensor 70 as will be described later with reference to aflowchart. In the latter case, the outside air temperature sensor 70functions as the decrease-in-quality-of-heat-absorbed detecting means.Specifically, if the outside air temperature is equal to or lower than−15° C. (which may be a first predetermined value), the decision is madethat it is so difficult to absorb heat using the exterior heat exchanger33 that the heating capacity has decreased significantly. On the otherhand, if the outside air temperature is equal to or lower than −20° C.(which may be a second predetermined value), then the decision is madethat it is almost impossible to absorb heat using the exterior heatexchanger 33 and no heating operation can be performed.

The air-conditioning controller 22 further includes adegree-of-heating-requested detecting section 22 b, which is provided todetect what degree of heating is requested when a heating operation isgoing to be started. In detecting the degree of heating requested, thetarget temperature of the air-conditioning air blowing out of theinterior air-conditioning unit 21 is compared to the real temperature ofthe air actually blowing out, and the decision is made that the lowerthe real temperature, the higher the degree of heating requested shouldbe and that the closer the real and target temperatures are, the lowerthe degree of heating requested should be. In this case, the targettemperature is calculated by the air-conditioning controller 22 based onthe temperature setting by the occupant and the outside air temperature,for example. Meanwhile, the real temperature may be obtained by havingthe temperature of the air-conditioning air in the vicinity of theblowout port measured by the temperature sensor, for example. Or thedecision may also be made that the higher the occupant's temperaturesetting, the higher the degree of heating requested should be.

Next, the procedure of control to be performed by the air-conditioningcontroller 22 will be described. Although not shown, in the mainroutine, if the outside air temperature (TG) detected by the outside airtemperature sensor 70 is lower than 0° C., the operation modes of theheat pump device 20 are switched into a heating operation mode. In theheating operation mode, a heat mode is mostly selected as the blowoutmode of the interior air-conditioning unit 21. Also, the air-mix door 62is operated so that the temperature of the blown air becomes as high asthe target temperature. Examples of the heating operation modes includethe normal heating operation mode, the first hot gas heating operationmode, the second hot gas heating operation mode, and therefrigerant-heated heating operation mode.

If the outside air temperature (TG) is within the range of 0° C. to 25°C., the air-conditioning controller 22 allows for performing heatingwhile dehumidifying. However, if the outside air temperature (TG) ishigher than 25° C., then the operation modes of the heat pump device 20are switched into the cooling operation mode.

If a heating operation mode has been selected in the main routine, theheating operation subroutine control shown in FIG. 14 is performed. Inperforming the heating operation subroutine control, first, in Step SA1,the outside air temperature TG detected by the outside air temperaturesensor 70 is loaded with the refrigerant heater 35 turned OFF. Next, theprocess proceeds to Step SA2 to determine whether or not the quantity ofheat absorbed by the exterior heat exchanger 33 has decreased. In thisembodiment, the quantity of heat absorbed by the exterior heat exchanger33 is detected by the outside air temperature sensor 70. If the outsideair temperature is equal to or lower than −15° C. (which may be a firstpredetermined value), the quantity of heat absorbed by the exterior heatexchanger 33 has decreased so much that the heating capacity maintainedby absorbing heat from the outside air would deteriorate significantly.That is why in that case, the process proceeds to Step SA3 to perform ahot gas heating operation mode selection processing.

Note that the determination may be made by the frosting detectingsection 22 a whether or not the quantity of heat absorbed by theexterior heat exchanger 33 has decreased. In that case, in Step SA2, thedetermination is made based on the amount of frost deposited in theexterior heat exchanger 33.

In Step SA3, first of all, the degree-of-heating-requested detectingsection 22 b determines whether the degree of heating requested is highor low. If the degree of heating requested turns out to be high, theprocess proceeds to Step SA4 to switch the operation modes of the heatpump device 20 into the first hot gas heating operation mode. As aresult, a heating operation may be performed without absorbing heat fromthe outside air.

Next, the process proceeds to Step SA5 to load the inside airtemperature TR that has been detected by the inside air temperaturesensor 75. Subsequently, in Step SA6, a determination is made whetherthe inside air temperature TR is higher than 20° C. If the inside airtemperature TR is higher than 20° C., it means that the air in thevehicle cabin has already been conditioned and heated to a sufficientdegree. Thus, in that case, the process goes back to Step SA3 to selecta hot gas heating operation mode again based on the degree of heatingrequested.

On the other hand, if the inside air temperature TR has turned out inStep SA6 to be lower than 20° C., then the process proceeds to Step SA7to determine whether or not the outside air temperature TG is equal toor lower than −20° C. If the decision made been made in Step SA7 thatthe outside air temperature TG is equal to or lower than −20° C., itmeans that it is almost impossible to absorb heat using the exteriorheat exchanger 33 and no heating can be performed by absorbing heat fromthe outside air. Thus, in that case, the process proceeds to Step SA8 toturn the refrigerant heater 35 ON and switch the operation modes of theheat pump device 20 into the refrigerant-heated heating operation mode,and then the process proceeds to END.

On the other hand, if the decision has been made in Step SA7 that theoutside air temperature TG is higher than −20° C., then heat can stillbe absorbed a little from the outside air, and the process goes back toStep SA3 with the refrigerant heater 35 kept OFF.

If the degree of heating requested has turned out to be low in Step SA3of selecting the hot gas heating operation mode, then the processproceeds to Step SA9 to switch the operation modes of the heat pumpdevice 20 into the second hot gas heating operation mode, and then theprocess proceeds to END.

On the other hand, if the answer to the query of the processing step SA2is NO and if the outside air temperature TG is higher than −15° C., thenheating may be performed by absorbing heat from the outside air withoutperforming a hot gas heating operation. In that case, first of all, theprocess proceeds to Step SA10 to make a frosting determination. Thisfrosting determination is made based on the degree of frosting in theexterior heat exchanger 33 that has been detected by the frostingdetecting section 22 a to determine whether the degree of frosting inthe exterior heat exchanger 33 is high or low. If the degree of frostingin the exterior heat exchanger 33 has turned out to be high in StepSA10, then the process proceeds to Step SA11 to switch the operationmodes of the heat pump device 20 into the defrosting operation mode.This defrosting operation mode will be described later.

After the air conditioner has operated in the defrosting operation mode,the process proceeds to Step SA12 to make a defrosting determination.The defrosting determination may be made by the frosting detectingsection 22 a to determine whether the frost in the exterior heatexchanger 33 has melted yet. If the decision has been made in Step SA12that the exterior heat exchanger 33 has already been defrosted, theprocess proceeds to END. On the other hand, if the decision has beenmade in Step SA12 that the exterior heat exchanger 33 has not beendefrosted yet, then the process goes back to Step SA10.

On the other hand, if the decision has been made in Step SA10 that thedegree of frosting is low, then a switch is made into the normal heatingoperation mode.

The heating operation subroutine control is performed as describedabove. If the operation modes have been switched in Step SA11 into thedefrosting operation mode, then the subroutine control shown in FIG. 15is performed. In Step SB1 of the flowchart shown in FIG. 15, adetermination is made whether or not the outside air temperature TGdetected by the outside air temperature sensor 70 is lower than 0° C. Ifthe answer to the query of the processing step SB1 is NO (i.e., if theoutside air temperature TG is equal to or higher than 0° C.), theprocess proceeds to Step SB2 to determine the degree of heatingrequested. That is to say, the degree-of-heating-requested detectingsection 22 b determines whether the degree of heating requested is highor low. If the degree of heating requested has turned out to be high,the process proceeds to Step SB3 to switch the operation modes of theheat pump device 20 into the gentle defrosting operation mode. In thegentle defrosting operation mode, no refrigerant flows through theexterior heat exchanger 33, but the frost in the exterior heat exchanger33 can still be melted by absorbing heat from the outside air, becausethe outside air temperature is higher than 0° C. On the other hand, ifthe degree of heating requested has turned out to be low in Step SB2,the process proceeds to Step SB4 to switch the operation modes of theheat pump device 20 into the powerful defrosting operation mode.Although the heating capacity is lower in the powerful defrostingoperation mode than in the gentle defrosting operation mode, theoccupant's comfortableness is not affected, because the degree ofheating requested is low.

Thereafter, the process proceeds to Step SB5 to determine whether or notthe refrigerant heater 35 is needed. This determination may be made bythe degree-of-heating-requested detecting section 22 b. If the decisionhas been made by the degree-of-heating-requested detecting section 22 bthat an even higher degree of heating is now requested, the processproceeds to Step SB6 to turn the refrigerant heater 35 ON and thenproceeds to END. On the other hand, if the degree-of-heating-requesteddetecting section 22 b has not found the degree of heating requested sohigh, the process proceeds to END. Optionally, this processing step SB2may be omitted. In that case, if the outside air temperature has turnedout in Step SB1 to be equal to or higher than 0° C., then a switch willbe made into the gentle defrosting operation mode.

On the other hand, if the answer to the query of the processing step SB1is YES (i.e., if the outside air temperature TG is less than 0° C.),then the process proceeds to Step SB7 to determine the degree of heatingrequested in the same way as in Step SB2. If the degree of heatingrequested has turned out to be high in Step SB7, then the processproceeds to Step SB8 to switch, according to the degree of heatingrequested, the operation modes of the heat pump device 20 into a modeselected from the group consisting of the moderate defrosting operationmode, the first heating-dominant defrosting operation mode, and thesecond heating-dominant defrosting operation mode. If the decision hasbeen made that the degree of heating requested is even higher, then theoperation modes are switched into the first or second heating-dominantdefrosting operation mode. On the other hand, if the degree of heatingrequested has turned out to be low in Step SB7, then the processproceeds to Step SB9 to switch the operation modes of the heat pumpdevice 20 into the powerful defrosting operation mode. Then, the processproceeds to END by way of Step SB5.

Optionally, in Step SA11 of the flowchart shown in FIG. 14, the switchbetween the gentle and powerful defrosting operation modes may becontrolled in the defrosting operation mode based on the flowchart shownin FIG. 16. In Step SC1 of this flowchart, the outside air temperatureTG detected by the outside air temperature sensor 70 is loaded. Next,the process proceeds to Step SC2 to make a frosting determination. Thefrosting determination may be made by the frosting detecting section 22a to determine whether the amount of frost deposited is less than, orequal to or greater than, a predetermined amount. If the amount of frostdeposited has turned out to be less than the predetermined amount, theprocess proceeds to Step SC3 to switch the operation modes of the heatpump device 20 into the gentle defrosting operation mode. On the otherhand, if the amount of frost deposited is equal to or greater than thepredetermined amount, the process proceeds to Step SC4 to switch theoperation modes of the heat pump device 20 into the powerful defrostingoperation mode. That is to say, if the amount of frost deposited is lessthan the predetermined amount, it means that the amount of frostdeposited is small enough to be easily melted even in the gentledefrosting operation mode. Meanwhile, the amount of frost deposited thatis equal to or greater than the predetermined amount is too large anamount of frost to be sufficiently melted in the gentle defrostingoperation mode.

Optionally, the air-conditioning controller 22 may be configured toselect a hot gas heating operation mode based on the quality of wetvapor of the refrigerant that has been detected by thequality-of-wet-vapor detecting sensor 80. That is to say, either thepowerful defrosting operation mode or the gentle defrosting operationmode is selected to prevent the motor-driven compressor 30 fromoperating in a wet condition.

Also, if the charge level of the traction battery B detected by thebattery level detecting sensor 81 is equal to or smaller than apredetermined value, the air-conditioning controller 22 may prohibit therefrigerant heater 35 from being activated. For example, the“predetermined value” may be a charge level of 30% of the battery's fullcapacity.

Furthermore, the air-conditioning controller 22 may also be configuredto allow the refrigerant heater 35 to be activated if it has beendetected that the air needs heating and that the traction battery B isnow being charged by the charging state detecting sensor 82.

Alternatively, the air-conditioning controller 22 may determine, in StepSA6, whether or not the air condition in the vehicle cabin is goodenough to meet the degree of heating requested detected by thedegree-of-heating-requested detecting section 22 b. If the decision hasbeen made that the air condition in the vehicle cabin is not good enoughto meet the degree of heating requested, then the refrigerant heater 35may be activated in Step SA8.

Still alternatively, the air-conditioning controller 22 may activate theheat pump device 20 so that the first hot gas heating operation mode isselected at the beginning of heating if it is difficult to absorb heatfrom the outside air.

Yet alternatively, the air-conditioning controller 22 may control thesecond pressure reducing valve 53 so that the valve 53 operates in theclosing direction to exhibit a pressure reduction function in the gentledefrosting operation mode and may control the second pressure reducingvalve 53 so that the valve 53 operates in the opening direction in thepowerful defrosting operation mode compared to the gentle defrostingoperation mode. Controlling the second pressure reducing valve 53 sothat the valve 53 operates in the opening direction in the powerfuldefrosting operation mode cuts down the pressure loss caused by therefrigerant and allows a high-temperature, high-pressure refrigerant toflow toward the exterior heat exchanger 33 and melt the frost there. Inaddition, making the second pressure reducing valve 53 exhibit such apressure reduction function in the gentle defrosting operation modeallows for performing a hot gas heating operation, thus achieving someheating capacity without using the exterior heat exchanger 33.

Furthermore, the air-conditioning controller 22 may control the blower65 so that the volume of the air blown decreases during the defrostingoperation compared to during the heating operation.

Furthermore, if the decision has been made that the air condition in thevehicle cabin is not good enough to meet the degree of heating requesteddetected by the degree-of-heating-requested detecting section 22 b, theair-conditioning controller 22 may activate the PTC heater 67.

As can be seen from the foregoing description, if the quantity of heatabsorbed by the exterior heat exchanger 33 has decreased, a vehicle airconditioner 1 according to this embodiment may switch the operationmodes into a first hot gas heating operation mode in which therefrigerant discharged from the motor-driven compressor 30 is allowed toflow through the downstream and upstream interior heat exchangers 31 and32, bypass the exterior heat exchanger 33, and then be sucked into themotor-driven compressor 30 after the pressure has been reduced or asecond hot gas heating operation mode in which the refrigerantdischarged from the motor-driven compressor 30 is allowed to flowthrough the downstream interior heat exchanger 31, bypass the upstreaminterior heat exchanger 32, further bypass the exterior heat exchanger33, and then be sucked into the motor-driven compressor 30 after thepressure has been reduced. As a result, even if it is difficult toabsorb heat using the exterior heat exchanger 33 when heating isrequested, the vehicle cabin may be heated with the capacity adjustedaccording to the situation and with the dissipation of energy reduced.

In addition, the comfortableness in the vehicle cabin is increased byswitching into the first hot gas heating operation mode if the degree ofheating requested is high or into the second hot gas heating operationmode if the degree of heating requested is low.

Furthermore, by making a switch between the first and second hot gasheating operation modes in accordance with the quality of wet vapor ofthe refrigerant sucked into the motor-driven compressor 30, thereliability of the heat pump device 20 is increased with themotor-driven compressor 30 prevented from operating in a wet condition.

Furthermore, if the quantity of heat absorbed by the exterior heatexchanger 33 is even smaller, the refrigerant heater 35 may be activatedto switch the modes into a hot gas heating operation mode. This thusensures some heating capacity.

Moreover, a decrease in the quantity of heat absorbed by the exteriorheat exchanger 33 may be detected by an outside air temperature sensor70, thus allowing for detecting a decrease in the quantity of heatabsorbed with reliability and at a low cost.

On top of that, a decrease in the quantity of heat absorbed by theexterior heat exchanger 33 is detected by the frosting detecting section22 a of the exterior heat exchanger 33. This allows for performing acontrol depending on the condition of the exterior heat exchanger 33.

Furthermore, the refrigerant heater 35 is implemented as an electricheater, thus allowing for providing comfortable air conditioning with avehicle air conditioner 1 mounted on an electric vehicle.

Furthermore, the refrigerant heater 35 is prohibited from beingactivated if the charge level of the vehicle's traction battery B islow, thus allowing for increasing the distance to empty when the vehicleair conditioner is mounted on an electric vehicle.

Furthermore, if the traction battery B is being charged, the refrigerantheater 35 is activated, thus allowing for ensuring some heating capacitybefore the vehicle starts to travel and after the vehicle has traveledand increasing the occupant's comfortableness. In addition, when thevehicle air conditioner is mounted on an electric vehicle, the distanceto empty is hardly affected.

Furthermore, the PTC heater 67 is activated if the decision has beenmade that the degree of heating requested will not be reached even byperforming a hot gas heating mode of operation. This thus allows forincreasing the occupant's comfortableness.

Furthermore, the operation modes are switched into a second hot gasheating operation mode at the beginning of heating, thus resulting in anincrease in quickness of heating and an increase in the occupant'scomfortableness.

In the embodiments described above, the bypass switching valve 56 of theheat pump device 20 is configured as a three-way valve. However, thebypass switching valve 56 may also be a combination of two on-off valves77 and 78 as in the variation shown in FIG. 17 or any other means forswitching the bypass pipe BP may be used instead.

Also, in the embodiments described above, the first and second flow pathswitching valves 50 and 51 of the heat pump device 20 are bothconfigured as three-way valves. However, either or both of the valves 50and 51 may be a combination of two on-off valves. Any flow pathswitching means may be used without particular limitation.

Also, in the embodiments described above, the vehicle air conditioner 1is supposed to be mounted on an electric vehicle. However, this is onlyan example of the present invention. The vehicle air conditioner 1 mayalso be mounted on various other types of automobiles such as a hybridcar including an engine and a traction motor.

Note that each and every embodiment described above is just an examplein any respects and should not be construed to be a limiting one.Besides, any variations or modifications falling within the range ofequivalents to the claims to be described below are all encompassedwithin the scope of the present invention.

As can be seen from the foregoing description, a vehicle air conditioneraccording to the present invention may be mounted on electric vehiclesand hybrid vehicles, for example.

The invention claimed is:
 1. A vehicle air conditioner comprising: aheat pump device including a compressor that compresses a refrigerant, afirst interior heat exchanger provided inside a vehicle cabin, a secondinterior heat exchanger provided inside the vehicle cabin and upstreamof the first interior heat exchanger in an airflow direction, anexterior heat exchanger provided outside the vehicle cabin, and apressure reducing valve, the heat pump device being formed by connectingtogether the compressor, the first and second interior heat exchangers,the pressure reducing valve and the exterior heat exchanger viarefrigerant piping, the heat pump device further including a bypass pipethrough which the refrigerant is bypassed around the exterior heatexchanger, the heat pump device being switchable between multipleoperation modes; an interior air-conditioning unit which houses thefirst and second interior heat exchangers and which includes a blowerthat blows air-conditioning air to the first and second interior heatexchangers, the interior air-conditioning unit being configured toproduce conditioned air and supply the conditioned air into the vehiclecabin; and an air-conditioning controller configured to control the heatpump device and the interior air-conditioning unit, wherein the airconditioner further includes an exterior heat exchanger temperaturesensor for determining whether or not the quantity of heat absorbed bythe exterior heat exchanger has decreased during heating, and adegree-of-heating-requested detecting section for detecting the degreeof heating requested, the heat pump device includes a plurality ofvalves for switching a refrigerant channel between a first hot gasheating operation mode in which at least the refrigerant discharged fromthe compressor is allowed to flow through the first and second interiorheat exchangers so that each of these interior heat exchangers functionsas a radiator, be bypassed around the exterior heat exchanger withpressure reduced by the pressure reducing valve, and then be sucked intothe compressor, and a second hot gas heating operation mode in which therefrigerant discharged from the compressor is allowed to flow throughthe first interior heat exchanger, be bypassed around the secondinterior heat exchanger, be further bypassed around the exterior heatexchanger after pressure has been reduced by the pressure reducingvalve, and then be sucked into the compressor, if the exterior heatexchanger temperature sensor has sensed that the quantity of heatabsorbed by the exterior heat exchanger is equal to or smaller than afirst predetermined value, and the degree-of-heating-requested detectingsection has found the degree of heating requested high, theair-conditioning controller switches the plurality of valves and makesthe heat pump device operate in the first hot gas heating operationmode, and if the exterior heat exchanger temperature sensor has sensedthat the quantity of heat absorbed by the exterior heat exchanger isequal to or smaller than a first predetermined value, and thedegree-of-heating-requested detecting section has found the degree ofheating requested low, the air-conditioning controller switches theplurality of valves and makes the heat pump device operate in the secondhot gas heating operation mode.
 2. The vehicle air conditioner of claim1, wherein in both the first hot gas heating operation mode and thesecond hot gas heating operation mode, the refrigerant of which thepressure has been reduced by the pressure reducing valve is sucked intothe compressor without passing through the heat exchanger.